The present invention relates to a system and method for cooling the shaft of a gear pump rotor in which a cooling medium is supplied axially through the shaft.
Because of the rheological characteristics of the lubricating medium, particularly when a conveying medium is used as a lubricating medium of slide bearings of the rotors, it is expedient in many applications of gear pumps to provide a shaft cooling or a lubricating medium cooling in order to dissipate the heat generated in the bearings, particularly in the slide bearings. As a result, a lower bearing temperature is achieved.
Normally, a shaft cooling system has an extremely simple construction. As illustrated in FIG. 1, which is a simplified axial sectional view of a known gear pump rotor 1, the shaft 3 has an axial bore 5 which passes through both bearing areas on the projecting shaft sections 7 as well as the shaft area 7.sub.v in the toothing area. In the following, the toothing area 7.sub.v is that area of the rotor shaft which is situated radially under the toothing irrespective of whether the gear wheel and the shaft are constructed as one part or as multiple parts.
A deflecting tube 11 projects into the axial bore 5, almost to the one-sided bore end 9. By way of a rotary sealing connection which is not shown, the cooling medium is fed to the deflecting tube 11, flows through this tube in an axial manner, is radially deflected at the end of the tube 11 in order to axially flow back in the countercurrent or vice versa. According to the preceding sign of the temperature difference, the cooling medium absorbs heat on its flow path or conveys heat. Reference is made in this respect to German Patent Document DE-A- 42 11 516.
A significant disadvantage of this cooling approach is the fact that, except for the cooling medium temperature which rises along the length of the bore and except for the different radial heat currents which normally flow out of the areas of the bearing and toothing areas, the shaft 7, 7.sub.v is cooled without any differences. This may result in a cooling effect in the area of the toothing 13 which results in an undesirably extensive lowering of the temperature level in the tooth base.
It is an object of the present invention to eliminate this disadvantage.
This object is achieved according to the invention by means of a cooling method of the initially mentioned type, wherein a lower heat conduction to the cooling medium per axial dimension unit is established in a toothed area of the shaft than in other shaft areas to be cooled with respect to identical cylinder surfaces on the toothed and other shaft areas.
As the result of the fact that according to the invention, a lower heat conduction to the cooling medium per axial dimension unit in the toothed area of the shaft is provided, with a view to the same cylinder surfaces, than in the other shaft areas to be cooled, particularly the bearing areas, is now established, it is achieved that the above-mentioned disadvantageous cooling of the toothing is considerably reduced without any influence on the desired cooling effect, particularly in the bearing areas.
According to especially preferred embodiments, the advantageous results are achieved in a preferable manner in that a gas insulation, particularly an air insulation, is established in the toothing area 7.sub.v, and/or a solid-body insulation, and/or the cooling medium contact surface in the toothing area per axial dimension unit is reduced in comparison to the above-mentioned contact surface on shaft areas which are intended to be cooled.
With respect to a gear pump rotor of the initially mentioned type, the object on which the present invention is based is achieved by a construction with reduced cooling in the gear tooth areas.
Certain preferred embodiments of the gear pump rotor according to the invention include air insulation sections near the toothed area. Other embodiments include solid insulation sections near the toothed area. Yet other embodiments include a shaft and cooling tube configuration with reduced heat conduction area in the area of the gear toothing.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.